Regenerative or recuperative furnaces having melting and fining zones have been commonly employed to manufacture glass. The regenerative or recuperative furnaces, unlike other types of furnaces, employ at least one regenerator or recuperator in operating air-fuel burners. At least one regenerator or recuperator, which may come in many different shapes and sizes, serves to preheat air used in the air-fuel burners. In the regenerator the preheating is generally accomplished by transferring the heat in the existing waste gas from a melting chamber to refractory bricks stacked in a checkerboard fashion. The bricks, in turn, give up their heat to the incoming air which will be used in combusting the fuel. Commonly, the recuperator may consist generally of a double wall tubing in which the off gas from the melting chamber flows in the central tube either countercurrent or concurrent to the air which is passing through the annulus. The performance of the regenerator or recuperator, however, may deteriorate with time because the regenerator or recuperator may be partially plugged or destroyed when it is subject to the waste gas containing chemical contaminants for a long period. The partially plugged or destroyed regenerator or recuperator adversely affects the performance of air-fuel burners, thereby decreasing the glass production rate and fuel efficiency.
It has been known, therefore, to employ oxygen-fuel burners, in a number of furnaces to supplement or totally replace the air-fuel burners. The oxygen-fuel burners have been designed to produce a flame and heat transfer similar to that of convention air-fuel burners. Specifically, the oxygen fuel burners are designed to fire parallel or substantially parallel to the surface of the glass. These burners transfer heat upward into the furnace crown and surrounding refractories as well as into the glass. Heat transfer is achieved by direct radiation from the flame and by re-radiation from the refractory superstructure of the glass furnace. Little heat is transferred to the glass by convection or conduction. The capacity of the glass furnace is limited by the highest refractory temperature within the melting chamber. Accordingly, one concern in the use of oxygen-fuel burners has been the risk associated with the high temperature of the burners and overheating of the refractory roof and walls of the furnace.
The present invention utilizes the higher flame temperature and lower mass flow rate achievable with oxygen-fuel combustion to significantly increase the heat transfer into the glass while maintaining refractory temperatures within operating limits. This is accomplished by utilizing at least one oxygen-fuel burner firing perpendicular or substantially perpendicular to the glass surface rather than in the conventional parallel configuration. By firing the burners perpendicular to the glass surface the convective and radiant properties of the flame are utilized to transfer energy to the raw glass-forming material rather than radiant heat transfer only. Accordingly, the luminosity and high temperature portion of the flame is placed in close proximity if not in direct contact with the raw glass-forming material to increase heat transfer via radiation. With radiation being an exponential function of distance from the heat source, the heat transfer by radiation is much greater in the glass melting furnace in accordance with the present invention than conventional furnaces. In addition, the impingement of the high temperature flame onto the raw glass forming material substantially increases the heat transfer via convection at the area of impingement of the flame. Consequently, the increased rate of heat transfer to the glass and batch results in a very substantial increase in the rate of melting and fining the glass. Furthermore, because the majority of the heat transfer is directly from the higher temperature impinging flame and not from the refractory, the melting capacity of the glass furnace is increased, without thermal deterioration of the refractory.
Accordingly, it is an object of the invention to increase the melting capacity of a glass furnace without increasing the risk of overheating the roof and walls of the furnace. It is another object of the invention to maintain a particular glass production rate without the use of regenerators or recuperators. It is a further object of the invention to reduce the formation of NOx during the glass melting. Yet another object of the present invention is to reduce the size of glass furnace required per given capacity over a conventional air-fuel glass furnace or a conventional oxygen-fuel glass furnace. Still another object of the present invention is to reduce the total energy required per ton of glass melted over conventional air-fuel glass furnaces. Another object of the present invention is to provide a glass furnace that permits better utilization of capacity and more flexibility of operation thus reducing melter capital cost per ton of glass produced.